It's this thread https://developer.apple.com/forums/thread/715103 I've posted my own description of it here again because I have virtually never downgraded macOS and am totally new to mac things. And because it took 10 minutes unboxing the m2 mac, and another 10 minutes to trigger the bug (after some time to install Xcode, offline). I'll use the feedback assistant to give my vote for working on the issue, I guess it could actually happen quite often. Will use the Report Navigator, or disable 'show live issues' as they advice in the thread. I didn't know the impact on incremental compilation etc. Pretty sure in 14.3 the issue should be gone.

Have to admit that I haven't disabled live issues in the settings, because I don't know what it would do at all, last time I used Xcode was ages ago. Issues or errors will be shown when a new build is triggered, but I couldn't imagine how well or not this works regarding incremental compilation, because someone wrote that this solution is tedious. The live issue is gone ATM, so, thank you for your consideration and have a happy Xcode.